Power supply control device

ABSTRACT

A power supply control device, by which a plurality of switching power supply circuits of different properties are operated under switching conditions respectively fitted therefor simultaneously with the prevention of an occurrence of what is called a low-frequency switching beat phenomenon, thereby achieving the miniaturization and the increasing of the efficiency of a power supply unit. To synchronize the timing of switching operations among control systems or units of the power supply control device, the control device of the multi-channel type or the control device having a master-slave function is used. Further, a frequency divider circuit or a frequency multiplier circuit is connected to a comparator of such a control device. Thereby, although synchronizing the timing among the switching operations, a plurality of pulse output signals of different frequencies are outputted from the control systems or the control units. Incidentally, a frequency divider circuit or a frequency multiplier circuit may be added to an oscillation circuit of the control device, instead of connecting the frequency divider circuit or the frequency multiplier circuit to the comparator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a power supply control devicefor driving a plurality of switching power supply circuits which areincorporated in a power supply unit and have different properties, forexample, switching-power-supply-circuits of the ordinary rectificationtype and of the synchronous rectification type by synchronizing theoperation timing among the circuits.

2. Description of the Related Art

In recent years, electronic devices have been miniaturized, while theperformance thereof and the range of functions thereof have beenenhanced. Thus, a power supply unit to be incorporated therein has aplurality of switching power supply circuits respectively correspondingto loads (namely, machines and circuits) of different properties. Here,note that generally, control integrated circuits of the pulse widthmodulation type are used for controlling the driving of the switchingpower supply circuits and that a power supply unit has control systemsof the number which corresponds to the number of the loads, namely, thenumber of the switching power supply circuits.

Meanwhile, when operating the plurality of switching power supplycircuits in a same power supply unit independently of one another, aninterference phenomenon (so called a switching beat), which is based ona plurality of switching operations, sometimes occurs in the unit. Thisis owing to the fact that, for example, when two switching power supplycircuits operate at switching frequencies f1 and f2, respectively, a lowfrequency corresponds to the difference (f1-f2) between the twoswitching frequencies is caused.

In order to prevent an occurrence of this low-frequency switching beatphenomenon, the conventional power supply unit synchronizes the timingof switching operations among a plurality of switching power supplycircuits that undergo independent output control. As practical examplesof this, there have been employed the following two means.

(1) Namely, a first one of the means adapted to employ a control deviceof the multi-channel type and use a unified reference waveform signal(namely, a triangular-wave voltage) as those of a plurality of controlsystems constituted in the control device.

(2) Further, a second one of the means adapted to employ a controldevices, each of which has a master-slave function, and to use one ofthe plural control devices as a master control device and operate thiscontrol device at a predetermined operation timing and at apredetermined oscillation frequency, and to use the rest of the controldevices as slave control devices and causes the slave control devices toreceive a synchronization signal from the master control device andoperate at operation timing synchronized with the master control deviceand at the same oscillation frequency as that of the master controldevice.

FIG. 1 schematically illustrates the control device corresponding to thefirst means, which is incorporated with the intention of preventing anoccurrence of such a low-frequency switching beat phenomenon, and apower supply unit employing this control device.

The control device CD of FIG. 1 is roughly composed of a first controlsystem CH1, a second control system CH2, a reference voltage supply 1,an oscillation circuit 2 and a protective circuit 3.

Here, the reference voltage supply 1 is adapted to output ahighly-stable voltage as a reference voltage level. Further, theoscillation circuit 2 is operative to output a triangular-wave voltageat a predetermined oscillation frequency. Moreover, the protectivecircuit 3 is operative to output an operation stopping signal so as toprotect the systems from a short in the output circuit and to prevent anoccurrence of a malfunction when a low level signal is inputted.

The reference voltage supply 1, the oscillation circuit 2 and theprotective circuit 3 are shared by the control systems.

The control system CH1 is used for driving and controlling a first powersupply circuit PS1 and is basically composed of an error amplifier Err1,a comparator Comp1 and an output buffer 1. An operation of this controlsystem CH1 is performed as follows. Namely, first, this control systemCH1 receives a feedback signal FB1 from the switching power supplycircuit PS1. Then, a voltage level represented by the received feedbacksignal FB1 is compared with a reference voltage (V_(RE) F) in the erroramplifier Err1, so that an error signal is obtained therein.Subsequently, this error signal is compared with a triangular-wavevoltage in the comparator Comp1, which generates a pulse output signalPO1 having on-duty in accordance with an output voltage thereof. Thispulse output signal PO1 is supplied to a switching device of theswitching power supply circuit PS1. Thereby, the switching power supplycircuit PS1 is driven and controlled in such a manner that an outputvoltage thereof remains constant.

The control system CH2 is used for driving and controlling a secondpower supply circuit PS2 and is basically composed of an error amplifierErr2, a comparator Comp2 and an output buffer 2. An operation of thiscontrol system CH2 is similar to the operation of the control systemCH1. Thus, the description of the operation of the control system CH2 isomitted.

Here, the protective circuit 3 is adapted to output an operationstopping signal when an abnormality occurs in the switching power supplycircuits PS1, PS2. When receiving this operation stopping signal, theoutput buffers Buf1, Buf2 prohibit pulse output signals PO1, PO2 frompassing therethrough. Thus, an operation of the switching power supplycircuit PS1 is stopped.

Referring next to FIG. 2, there is schematically shown control devicescorresponding to the second means and a power supply unit having thesecontrol devices, which are constituted for the purpose of preventing anoccurrence of low-frequency switching beat phenomenon.

In the power supply unit of FIG. 2, two switching power supply circuitPS3 and PS4 are driven and controlled by control devices MCD and SCD,respectively, independently of each other.

Here, the control device MCD is composed of: a control system, whichconsists of an error amplifier MErr, a comparator MComp and an outputbuffer MBuf; a reference voltage supply 11 for outputting a referencevoltage or signal; an oscillation circuit 12; and a protective circuit13. An operation of this control device MCD is performed as follows.Namely, the control device MCD receives a feedback signal FB3 from theswitching power supply circuit PS3. Subsequently, a voltage representedby this feedback signal FB3 is compared with a reference voltage (V_(RE)F) in the error amplifier MErr, so that an error signal is obtained.

Then, the comparator MComp compares the error signal with atriangular-wave signal sent from the oscillation circuit 12 and furtheroutputs a pulse output signal PO3 having on-duty in accordance with anoutput voltage thereof. This pulse output signal PO3 is supplied to aswitching device of the switching power supply circuit PS3. Thereby, theswitching power supply circuit PS3 is driven and controlled in such amanner that an output voltage thereof remains constant.

Here, the oscillation circuit 12 is operative to output asynchronization signal RSS (which is generally a voltage that is thesame as the triangular-wave voltage to be supplied to the comparatorComp1) to an external circuit simultaneously with supplying atriangular-wave voltage to the comparator MComp.

Further, the control unit SCD is composed of: a control system whichconsists of an error amplifier SErr, a comparator SComp and an outputbuffer SBuf; a reference voltage supply 21; an oscillation circuit 22;and a protective circuit 23. An operation of this control device SCD isfundamentally the same as of the control device MCD. The control deviceSCD, however, is different from the control device MCD, in which theoscillation circuit 12 of the control device MCD produces atriangular-wave voltage at independent operation timing and at thepredetermined oscillation frequency, in that the oscillation circuit 22of the control device SCD receives a synchronization signal (RSS) fromthe control device MCD and operates in such a way as to generate atriangular-wave voltage whose operation timing and oscillation frequencyare the same as those of the signal produced by the oscillation circuit12.

As is understood from this, in the case of the power supply unit of FIG.2, the control device MCD functions as the master control device, whilethe control device SCD functions as the slave control device.

The reduction in sizes of electronic devices in recent years results ingreat demand for the miniaturization of power supply units therefor.When miniaturizing the power supply units, the inductors and thecapacitors of the switching power supply circuits PS3 and PS4 are firstminiaturized. At that time, the switching frequency of the switchingdevice is set at a high value. This switching frequency is determinedaccording to the oscillation frequency of a triangular-wave voltageoutputted by the oscillation circuit 2, 12 or 22 of the control deviceCD, MCD or SCD. Although the generally used oscillation frequency isseveral hundreds kilohertz (kHz), an oscillation circuit, which providesan oscillation frequency of several megahertz (MHz), is currentlyavailable.

Meanwhile, because of the fact that batteries are used in electronicdevices as power source, the reduction in sizes of the electronicdevices to the portable sizes thereof also results in great demand for areduction in the power consumption of the power supply units therefor. Aproblem to be solved for the reduction in power consumption of the powersupply units to low levels is the improvement of the efficiency of eachof switching power supply circuits. Switching power supply units of thesynchronous rectification type are available as means for improving theefficiencies of the switching power supply circuits.

This switching power supply circuit of the synchronous rectificationtype employs a transistor as a rectifying device, instead of a diode. Aloss produced in the transistor due to a collector-to-emitter voltage inan on-state is less than a loss produced in the diode owing to a forwardvoltage (drop). Thus, theoretically, a loss produced in the rectifyingdevice is reduced. Thereby, the efficiency of the switching power supplycircuit can be enhanced. However, in the case of actually using atransistor as a rectifying device, losses are produced when on/offoperations thereof are performed. As the switching frequency becomeshigher, losses abruptly increase. As a result, in the case of switchingfrequencies of a certain range, a loss produced in the switching powersupply circuit of the synchronous rectifying type using a transistor ismore than a loss produced in the switching power supply circuit of theordinary type using a diode. Incidentally, it is known that in the caseof using semiconductor devices already on the market, the limit of theswitching frequency for increasing the efficiency of the switching powersupply circuit by employing the circuit of the synchronous rectificationtype is about 200 kHz.

Moreover, in the case of the circuit of the synchronous rectifying typeusing a transistor as the rectifying device, there is the necessity ofcomplementarily driving the transistor, which is employed as therectifying device, in synchronization with the operation of theswitching device. Thus, the switching power supply circuits furtherrequire circuits and components therefor.

Therefore, in the case of the switching power supply circuit employingthe synchronous rectification, the size of the circuit is large incompensation for the increasing of the efficiency thereof, in comparisonwith the case of employing the switching power supply of the ordinaryrectification type. Consequently, in the former case, the size of thepower supply unit is large.

To attain the miniaturization of the power supply unit and theincreasing of the efficiency thereof by achieving a good balancetherebetween, it is considered as necessary to suitably arrange theswitching power supply circuit of the ordinary rectification type andthe switching power supply circuit of the synchronous rectification typein the unit according to the characteristics of loads. For example, theminiaturization of the power supply unit is achieved by applying theswitching power supply circuit of the ordinary rectification type to aload whose power consumption is small, while the high efficiency of thepower supply unit is realized by applying the switching power supplycircuit of the synchronous rectification type to a load whose powerconsumption is large.

However, in the actual case of using the switching power supply circuitof the ordinary rectification type together with the switching powersupply circuit of the synchronous rectification type, the conventionalpower supply control device of FIG. 1 has a problem in that pulse outputsignals supplied from each of the control systems to the switching powersupply circuits has only one kind of a pulse frequency (a switchingfrequency).

The miniaturization of the power supply unit requires a high switchingfrequency, whereas the increasing of the efficiency thereof (synchronousrectification) requires a lower switching frequency. Namely, when thepulse output signals has only one kind of the pulse frequency under thiscondition in which the tendencies of the frequencies respectivelyrequired by the miniaturization and the increasing of the efficiency,respectively, are opposed to each other, one of the miniaturization andthe increasing of the efficiency has to be traded off for the otherthereof.

Similarly, in the case of the power supply control devices (MCD and SCD)of the master-slave type as shown in FIG. 2, in order to preventgeneration of a low frequency switching beat, the operation-timing andoscillation-frequency of a triangular-wave voltage outputted from theslave control device (SCD) are set in such a manner as to be the same asthose of a triangular-wave voltage outputted from the master controldevice (MCD). Thus, the same problems as in the case of the power supplycontrol circuit of FIG. 1 comes up. Consequently, one of theminiaturization and the increasing of the efficiency has to be tradedoff for the other thereof.

SUMMARY OF THE INVENTION

It is, accordingly, an object of the present invention to provide apower supply control device by which a plurality of switching powersupply circuits of different properties, which include those of theordinary rectification type and the synchronous rectification type, canbe operated under switching conditions respectively suitable therefor,thereby achieving a good balance between the miniaturization of a powersupply unit and the increasing of the efficiency thereof.

To achieve the foregoing object, in accordance with the presentinvention, there is provided a power supply control device of themulti-channel type/pulse-width modulation type that has a plurality ofcontrol systems in such a way as to control a plurality of power supplycircuits independently of one another and causes the plurality ofcontrol systems to share oscillation means for supplying a signal to thecontrol systems and synchronizes pulse output signals of the controlsystems with one another. Further, the pulse frequency of a pulse outputsignal of at least one of the plurality of power supply control devicesis divided by frequency divider means into a low frequency which is 1/nof a pulse frequency of other control systems ("n" is an integer).Alternatively, the pulse frequency of a pulse output signal of at leastone of the plurality of power supply control devices is multiplied byfrequency multiplier means into a high frequency which is n times apulse frequency of other control systems.

Further, in accordance with the present invention, there is providedanother power supply control device having a master-slave function,which is used as a master control device, which is adapted to output apulse output signal at an independent operation timing and at apredetermined pulse frequency and control at least one of a plurality ofpower supply circuits placed in juxtaposition with one another, or aslave control device which receives a synchronization signal from amaster control device and outputs a pulse output signal at an operationtiming and at a pulse frequency in synchronization with the mastercontrol device and control a power supply circuit other than the mastercontrol device. This power supply control device is provided withfrequency divider means or frequency multiplier means and is adapted tooutput a pulse output signal, whose pulse frequency is a low frequency,which is 1/n of the frequency of a pulse output signal outputted inresponse to a synchronization signal, or a high frequency which is ntimes the frequency of a pulse output signal outputted in response to asynchronization signal.

A first practical embodiment of the present invention is a power supplycontrol device of the multi-channel type having a plurality of controlsystems, at least one of which has a frequency divider circuit andoutputs a pulse output signal, whose pulse frequency is a low frequencythat is 1/n of the frequency of a pulse output signal of another controlsystem.

A second practical embodiment of the present invention is a power supplycontrol device of the multi-channel type having a plurality of controlsystems, at least one of which has a frequency multiplier circuit andoutputs a pulse output signal, whose pulse frequency is a high frequencythat is n times the frequency of a pulse output signal of anothercontrol system.

Incidentally, the frequency divider circuit and the frequency multipliercircuit are provided at output terminals of comparators or at inputterminals, to which reference waveform signals are applied, ofcomparators in the control system.

In the case of a third practical embodiment of the present invention, afrequency divider means or a frequency multiplier means is added to anoscillation circuit provided in a control device. Thereby, ahigh-frequency reference waveform signal and a low-frequency referencewaveform signal are obtained. By supplying the reference waveformsignals to control systems, a control system, which outputs ahigh-frequency pulse output signal, and another control system, whichoutputs a low-frequency pulse output signal, are formed therein.

A fourth practical embodiment of the present invention is a power supplycontrol device having a master-slave function, in which a frequencydivider or a frequency multiplier is connected to comparison means of amaster control unit or comparison means of a slave control unit.Further, high-frequency and low-frequency pulse output signals, whosepulse frequencies are at a ratio of 1 to n, are obtained from the masterand slave control units, respectively.

A fifth practical embodiment of the present invention is a power supplycontrol device having a master-slave function, in which a frequencydivider or a frequency multiplier is connected to an oscillation circuitof a master control unit or an oscillation circuit of a slave controlunit. Further, high-frequency and low-frequency pulse output signals,whose pulse frequencies are at a ratio of 1 to n, are obtained from themaster and slave control units, respectively.

In the case of a sixth practical embodiment of the present invention, afrequency divider means or a frequency multiplier means is provided atan oscillation circuit in a master control device. Thereby, first andsecond synchronization signals respectively having high and lowfrequencies, which are at a ratio of 1 to n, are generated. Further,high-frequency and low-frequency pulse output signals, whose pulsefrequencies are at a ratio of 1 to n, are respectively obtained frommaster and slave control devices, which operate in response to thesynchronization signal, or from slave control devices which also operatein response to the synchronization signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparent from the following description of preferred embodimentswith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout several views, and inwhich:

FIG. 1 is a block diagram showing a conventional power supply controldevice of the multi-channel type and conventional switching power supplycircuits thereof;

FIG. 2 is a block diagram showing a conventional power supply controldevice, which has a master-slave function, and conventional switchingpower supply circuits thereof;

FIG. 3 is a block diagram showing a first embodiment of the presentinvention, in which a frequency divider circuit is connected to acontrol system of a power supply control device of the multi-channeltype;

FIG. 4 is a block diagram showing a second embodiment of the presentinvention, in which a frequency divider circuit is connected to acontrol system of a power supply control device of the multi-channeltype;

FIG. 5 is a block diagram showing a third embodiment of the presentinvention, in which a frequency divider means is provided in anoscillation circuit of a power supply control device of themulti-channel type;

FIG. 6 is a block diagram showing a fourth embodiment of the presentinvention, in which a frequency multiplier circuit is connected to acontrol system of a power supply control device of the multi-channeltype;

FIG. 7 is a block diagram showing a fifth embodiment of the presentinvention, in which a frequency multiplier circuit is connected to acontrol system of a power supply control device of the multi-channeltype;

FIG. 8 is a block diagram showing a sixth embodiment of the presentinvention, in which a frequency multiplier means is provided in anoscillation circuit of a power supply control device of themulti-channel type;

FIG. 9 is a block diagram showing a seventh embodiment of the presentinvention, in which a frequency divider circuit is connected to a slavepower supply control device;

FIG. 10 is a block diagram showing an eighth embodiment of the presentinvention, in which a frequency divider means is provided in anoscillation circuit of a slave power supply control device;

FIG. 11 is a block diagram showing a ninth embodiment of the presentinvention, in which a frequency divider circuit is connected to a masterpower supply control device;

FIG. 12 is a block diagram showing a tenth embodiment of the presentinvention, in which a frequency divider means is provided in anoscillation circuit of a master power supply control device;

FIG. 13 is a block diagram showing an eleventh embodiment of the presentinvention, in which a frequency divider means is provided in anoscillation circuit of a master power supply control device;

FIG. 14 is a block diagram showing a twelfth embodiment of the presentinvention, in which a frequency multiplier circuit is connected to aslave power supply control device;

FIG. 15 is a block diagram showing a thirteenth embodiment of thepresent invention, in which a frequency multiplier means is provided inan oscillation circuit of the slave power supply control device;

FIG. 16 is a block diagram showing a fourteenth embodiment of thepresent invention, in which a frequency multiplier circuit is connectedto a master power supply control device;

FIG. 17 is a block diagram showing a fifteenth embodiment of the presentinvention, in which a frequency multiplier means is provided in anoscillation circuit of a master power supply device; and

FIG. 18 is a block diagram showing a sixteenth embodiment of the presentinvention, in which a frequency multiplier means is provided in anoscillation circuit of a master power supply device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail by referring to the accompanying drawings.

FIG. 3 is a block diagram illustrating the first embodiment of thepresent invention, namely, a power supply control device embodying thepresent invention, which can drive a plurality of switching power supplycircuits of different properties, for example, switching power supplycircuits of the ordinary rectification type and those of the synchronousrectification type under the conditions respectively suitable therefor.

In the power supply control device CD of FIG. 3, a control system 2a hasa frequency divider circuit div1 in addition to an error amplifier Err2,a comparator Comp2 and an output buffer Buf2.

Here, the frequency divider circuit div1 performs a frequency divisionon the switching frequency of a pulse output signal generated in thecomparator Comp2. As a result, the switching frequency of a pulse outputsignal PO2 outputted from a terminal pin D of the control system CH2a islower than that of a pulse output signal PO1 outputted from a terminalpin B of the control system CH1.

Such a power supply control device CD is used, namely, a switching powersupply circuit of the ordinary rectification type is driven andcontrolled by the control system CH1, and a switching power supplycircuit of the synchronous rectification type is driven and controlledby the control system CH2. Then, the switching power supply circuit ofthe ordinary rectification type can be miniaturized by increasing orraising the switching frequency thereof, while the efficiency of theswitching power supply circuit of the synchronous rectification type canbe enhanced by decreasing or lowering the switching frequency. Further,the two pulse output signals are different in switching frequency fromeach other, whereas the operations thereof are performed at the sameoperation timing. Thus, there is no fear that a switching beat occurs.

In the case of miniaturizing the power supply unit by raising orincreasing the oscillation frequency of a triangular-wave voltageoutputted from the oscillation circuit in the power supply unit in whichthe switching power supply circuits of the ordinary rectification typeand the synchronous rectification type are placed in juxtaposition, theoverall efficiency of the power supply unit can be greatly improved bythe frequency divider circuit.

Incidentally, in the case of the power supply control device CD of FIG.3, the frequency divider circuit div1 is connected to an output terminalof the comparator Comp2 so as to perform the frequency division on apulse output signal generated in the comparator Comp2. In contrast, evenin the case that the output terminal of the comparator Comp2 isconnected to the output buffer Buf2 and further, the frequency dividercircuit is connected to an output terminal of the output buffer Buf2,similar effects or advantages can be obtained.

Referring next to FIG. 4, there is shown the second embodiment of thepresent invention, namely, another power supply control device embodyingthe present invention. In the case of a control system CH2b of thecontrol device CD of FIG. 4, a frequency divider circuit div2 isconnected to an input terminal, at which a triangular-wave voltage isreceived, of a comparator Comp2, differently from the case of thecontrol system CH2a of the control device CD of FIG. 3, in which thefrequency divider circuit div1 is connected to an output side orterminal of the comparator Comp2.

In the case of the second embodiment, the frequency division isperformed on the frequency of the triangular-wave voltage, which isinputted to the comparator Comp2, by the frequency divider circuit div2.Thus, the frequency of a pulse output signal PO2 outputted from aterminal pin D of the control system CH2b is lower than that of thepulse output signal (PO1) outputted from the terminal pin B of thecontrol system CH1.

Therefore, the operation and effects of the control system CH2b of FIG.4 are similar to those of the control system CH2a of FIG. 3.Consequently, when the switching power supply circuit of the ordinaryrectification type is driven and controlled by the control system CH1and the switching power supply circuit of the synchronous rectificationtype is driven and controlled by the control system CH2b, both of theminiaturization of the power supply unit and the increasing of theefficiency thereof can be achieved simultaneously.

FIG. 5 illustrates the third embodiment of the present invention,namely, still another power supply control device. The frequency dividercircuits (div1 and div2) are connected to the control systems (CH2a andCH2b), respectively, in the case of the power supply control devices ofFIGS. 3 and 4, while the frequency divider means is added to theoscillation circuit 2a shared by the control systems in the case of thecontrol device of FIG. 5. Thus, the control device of FIG. 5 is adaptedso that two reference waveform signals, namely, a high-frequencytriangular-wave voltage and a low-frequency triangular-wave voltage areobtained in the oscillation circuit 2a. By inputting a high-frequencytriangular-wave voltage to the comparator Comp1 of the control systemCH1 and further inputting a low-frequency triangular-wave voltage to thecomparator Comp2 of the control system CH2, the control device CD ofFIG. 5 can obtain substantially the same operations and effects as ofthe control device CD of FIG. 4.

Incidentally, there are various circuit configurations (or systems) ofthe oscillation circuit for outputting a triangular-wave voltage.Generally, a process consisting of steps of generating arectangular-wave voltage from a d.c. voltage and converting therectangular-wave voltage to the triangular-wave voltage is performed.Thus, there have been devised two means for obtaining a low-frequencytriangular-wave voltage, namely, a first means of performing thefrequency division at the stage, at which a rectangular-wave voltage isproduced from the d.c. voltage, and a second means of performing thefrequency division at the stage, at which a triangular-wave voltage isproduced from the rectangular-wave voltage. Both of these two means maybe employed in the oscillation circuit 2a.

FIG. 6 illustrates a fourth embodiment of the present invention, namely,yet another power supply control device embodying the present invention.In the case of the power supply control device of FIG. 6, a controlsystem CH2c has a frequency multiplier circuit mull in addition to anerror amplifier Err2, a comparator Comp2 and an output buffer Buf2.Namely, the power supply control device of FIG. 6 performs an operation,which is reverse to the operation of the power supply control device ofFIG. 3, by replacing the frequency divider circuit div1 with thefrequency multiplier circuit mull. Consequently, the power supplycontrol device of FIG. 6 obtains two pulse output signals respectivelyhaving different frequencies, similarly as the power supply controldevice of FIG. 3.

Namely, the frequency multiplier circuit mull performs a multiplicationof the switching frequencies of the pulse output signals generated inthe comparator Comp2. As a result, the switching frequency of a pulseoutput signal PO2 outputted from a terminal pin D is higher than theswitching frequency of a pulse output signal PO1 outputted from aterminal pin B. Thus, the switching power supply circuit of thesynchronous rectification type is driven and controlled by the controlsystem CH1. Further, the switching power supply circuit of the ordinaryrectification type is driven and controlled by the control system CH2.Thus, the switching circuit of the ordinary rectification type can beminiaturized by raising or increasing the switching frequency thereof.On the other hand, the efficiency of the switching circuit of thesynchronous rectification type can be enhanced by lowering or decreasingthe switching frequency thereof.

Meanwhile, the fifth embodiment of the present invention, namely, stillanother power supply control device of FIG. 7 is obtained bysubstituting the frequency multiplier circuit mu12 for the frequencydivider circuit div2 of FIG. 4. Further, the sixth embodiment of thepresent invention, namely, yet another power supply control device ofFIG. 8 is obtained by replacing the oscillation circuit 2a of FIG. 5, towhich the frequency divider circuit is added, with an oscillationcircuit 2b to which a frequency multiplier means is added.

A pulse output signal PO2 outputted from a terminal pin D by the actionof the frequency multiplier circuit mu12 and the oscillation circuit 2bhas a pulse frequency which is higher than a pulse frequency of a pulseoutput signal PO1 outputted from a terminal pin B. Thus, in the controldevices of FIGS. 7 and 8, operations, which are reverse to those of thecontrol devices of FIGS. 4 and 5, are performed. Consequently, two pulseoutput signals respectively having two different frequencies areobtained, similarly as in the case of the control devices of FIGS. 4 and5.

Referring further to FIG. 9, there is shown the seventh embodiment ofthe present invention, namely, still another power supply control deviceembodying the present invention. Differently from the embodiments of thepresent invention of FIGS. 3 to 8, which are of the multi-channel typesimilarly as in the case of the conventional power supply unit of FIG.1, this power supply control device of FIG. 9 is of the type having amaster-slave function similarly as in the case of the conventional powersupply unit of FIG. 2.

The power supply control device SCD of FIG. 9 is a slave control deviceand has an error amplifier SErr, a comparator SComp, an output bufferSBuf and a frequency divider circuit div3 connected to an output side orterminal of the comparator SComp.

In principle, an oscillation circuit 22 receives a synchronizationsignal RSS from a master control device (not shown) and outputs atriangular-wave voltage similarly as an oscillation circuit of themaster control device does. Thus, the frequency of the pulse outputsignal generated in the comparator SComp is equal to that of a pulseoutput signal (PO3) outputted by the master control device. Thefrequency divider circuit div3, however, performs a frequency divisionon the pulse frequency of a pulse output signal generated in thecomparator SComp to thereby lower or decrease the pulse frequency. As aconsequence, the pulse frequency of a pulse output signal (PO4)outputted from a terminal pin D by the power supply control device SCDof FIG. 9 is lower than the pulse frequency of a pulse output signal(PO3) outputted by the master control device or of a pulse output signaloutputted by a slave control device (not shown) which operatesfaithfully in response to a synchronization signal outputted from themaster control device.

A switching power supply circuit of the synchronous type is driven andcontrolled by the power supply control device SCD of FIG. 9, whose pulseoutput signal has a low frequency, and in contrast, a switching powersupply circuit of the ordinary rectification type is driven andcontrolled by the master control device, whose pulse output signal has ahigh frequency. Then, the switching power supply circuit of the ordinaryrectification type can be miniaturized by increasing or raising theswitching frequency thereof, while the efficiency of the switching powersupply circuit of the synchronous rectification type can be enhanced bydecreasing or lowering the switching frequency.

Therefore, in the case of miniaturizing the power supply unit by raisingor increasing the oscillation frequency of a triangular-wave voltageoutputted from the oscillation circuit in the power supply unit in whichthe switching power supply circuits of the ordinary rectification typeand the synchronous rectification type are placed in juxtaposition, theoverall efficiency of the power supply unit can be greatly improved bythe frequency divider circuit.

Incidentally, in the case of the power supply control device SCD of FIG.9, the frequency divider circuit div3 is connected to an output terminalof the comparator SComp. In contrast, even in the case that the outputterminal of the comparator SComp is connected to the output buffer SBufand further, the frequency divider circuit div3 is connected to anoutput terminal of the output buffer Buf, similar effects or advantagescan be obtained.

FIG. 10 illustrates the eighth embodiment of the present invention,namely, yet another power supply control device embodying the presentinvention. In the case of the control device of FIG. 10, a frequencydivider means is added to an oscillation circuit 22a for outputting atriangular-wave voltage in accordance with a synchronization signal sentfrom a master control device.

In this case, the frequency of a triangular-wave voltage inputted to acomparator SComp is lowered by the frequency divider means. Thus, thefrequency of a pulse output signal PO4 generated in the comparator SCompis lower than the pulse frequency of a pulse output signal outputted bya master control unit or by another slave control device which operatesfaithfully in response to a synchronization signal sent from the mastercontrol device.

As a result, an operation of the power supply control device SCD of FIG.10 is similar to the operation of the power supply control device ofFIG. 9, so that the miniaturization and the increasing of the efficiencyof a power supply unit can be achieved.

Incidentally, in the case of using an oscillation circuit 22a of FIG.10, basically, the frequency division may be performed at any stage fromthe reception of a synchronization signal to the conversion to atriangular-wave voltage through the generation of a rectangular-wavevoltage, though the suitable stage may change according to the circuitconfiguration (or system) and the synchronization signal received fromthe master control device. Additionally, instead of integrally mountingthe frequency divider circuit with the oscillation circuit, thefrequency divider circuit may be formed separately from the oscillationcircuit. Further, the frequency divider circuit may be provided at asynchronization-signal receiving side terminal of the oscillationcircuit or at a triangular-wave-voltage-signal outputting side terminalthereof.

FIGS. 11 and 12 illustrate the ninth embodiment and the tenth embodimentof the present invention, respectively, namely, other power supplycontrol devices embodying the present invention. In the cases of theaforementioned control devices of FIGS. 9 and 10, the frequency dividercircuit div3 is connected to the power supply control device acting as aslave control device, and the frequency divider means is provided in theoscillation circuit 22a. In contrast, in the cases of the controldevices of FIGS. 11 and 12, the frequency divider circuit is connectedto the power supply control device serving as a master control device,and the frequency divider means is provided in the oscillation circuit.

In the case of the power supply control device MCD of FIG. 11, afrequency divider circuit div4 is connected to an output side orterminal of a comparator Mcomp of the control system, similarly as inthe case of the power supply control device SCD of FIG. 9.

In the oscillation circuit 12 of FIG. 11, the frequency of asynchronization signal RSS supplied to a slave control device is equalto that of a triangular-wave voltage supplied to the comparator Mcomp.Therefore, the pulse frequency of a pulse output signal generated in thecomparator MComp of FIG. 11 is equal to that of a pulse output signaloutputted by the slave control device which operates in accordance witha synchronization signal. However, because the frequency division isperformed on the pulse frequency of the pulse output signal by thefrequency divider circuit div4, the frequency of the pulse output signalPO3 outputted from a terminal pin F is lower than that of the pulseoutput signal outputted by the slave control device.

In the case of the power supply control device MCD of FIG. 12, afrequency divider means is added to the oscillation circuit 12a,similarly as in the case of the power supply control device SCD of FIG.10.

Here, in the case of the oscillation circuit 12a to which the frequencydivider means is added, the frequency of a triangular-wave voltage to befed to the comparator MComp is set in such a way as to be lower thanthat of the synchronization signal RSS to be supplied to a slave controldevice (not shown). Thereby, the pulse frequency of the pulse outputsignal PO3 outputted from the power supply control device MCD of FIG. 12is lower than that of the pulse output signal outputted by the slavecontrol device which operate according to the synchronization signalRSS.

FIG. 13 illustrates the eleventh embodiment of the present invention,namely, another power supply control device embodying the presentinvention. In the case of this power supply control device MCD of FIG.13, a frequency divider means is added to an oscillation circuit 12b.Further, the frequency of a synchronization signal RSS to be supplied toa slave control device is set in such a manner as to be lower than thatof a triangular-wave voltage to be supplied to a comparator MComp, incontrast with the control device of FIG. 12. Incidentally, assuming thatthere are a plurality of slave control devices (not shown) and powersupply control devices used for switching power supply circuits of theordinary rectification type and power supply control devices used forswitching power supply circuits of the synchronous rectification typecoexist, the control device of FIG. 13 is adapted so that both of ahigh-frequency synchronization signal RO1 and a low-frequencysynchronization signal RO2 can be obtained from the oscillation circuit12b.

FIGS. 14 to 18 illustrate the twelfth to sixteenth embodiments of thepresent invention, respectively.

In the case of the power supply control devices of FIGS. 9 to 13, thepulse frequency of a pulse output signal outputted from one of masterand slave control devices is changed by a frequency divider circuit or afrequency divider means. Power supply control devices of FIGS. 14 to 18are adapted so that the pulse frequency of a pulse output signal of oneof the master and slave control circuits is changed by using frequencymultiplier circuits (or means) instead of these frequency dividercircuits (or means).

Namely, the control device of FIG. 14 is a slave control device SCD inwhich a frequency multiplier circuit mul3 is connected to an outputterminal of a comparator SComp.

Further, the control device of FIG. 15 is a slave control device SCDemploying an oscillation circuit 22b, to which a frequency multipliermeans is added, as the oscillation circuit.

The control device of FIG. 16 is a master control device MCD in which afrequency multiplier circuit mul4 is connected to an output terminal ofa comparator MComp.

The control device of FIG. 17 is a master control device MCD in which anoscillation circuit 22c, to which a frequency multiplier means is added,as an oscillation circuit.

The control device of FIG. 18 is a master control device MCD in which anoscillation circuit 22d, to which a frequency multiplier means is added,as an osillation circuit. Incidentally, in the case of the controldevice of FIG. 17, the multiplication of the frequency of atriangular-wave voltage is performed. In contrast, in the case of thecontrol device of FIG. 18, the multiplication of the frequency of thesynchronization signal RSS to be supplied to a slave control device isperformed. The control device of FIG. 18 is different in this respectfrom the control device of FIG. 17.

In the case of operations of the power supply control devices of FIGS.14 to 18, the pulse frequency is set in such a manner as to be high, incomparison with the case of the power supply control devices of FIGS. 9to 13 in which the pulse frequency is set in such a way as to be low.The remaining operations, namely, the fundamental control operations ofthe power supply control devices of FIGS. 14 to 18 are similar to thecorresponding operations of the power supply control devices of FIGS. 9to 13. Therefore, the description of the remaining operations of thecontrol devices of FIGS. 14 to 18 is omitted herein.

Incidentally, in the foregoing description of the embodiments of thepresent invention of FIGS. 3 to 8, the control devices, each of whichcontains two control systems, have been described as examples of thepower supply control devices of the multi-channel type. The presentinvention, however, is not limited to these embodiments. Needless tosay, the present invention can be applied to a control device providedwith an arbitrary (or unspecific) number of control systems. Similarly,in the description of the embodiments of the present invention of FIGS.9 to 18, it is assumed that the power supply control device is of thesingle-channel type provided with a single control system. However, thepower supply control device of the multi-channel type provided with twocontrol systems or more may be used instead of the power supply controldevice of the single-channel type.

Further, the power supply unit, which is provide with an arbitrary orunspecific number of power supply circuits, may have a plurality ofcontrol devices, each of which is provided with a frequency dividermeans or a frequency multiplier means. In such a case, there is nonecessity to set the frequency division ratios of the frequency dividermeans or the frequency multiplication ratio of the frequency multipliermeans at a uniform value. Namely, the frequency division ratios or thefrequency multiplication ratios may be set in accordance with thecharacteristics of switching power supply circuits to be driven andcontrolled.

As described above, in the case of the power supply control devices ofthe multi-channel type or having the master-slave function, frequencydivider means or frequency multiplier means are provided in apredetermined control system (or a predetermined control unit) orpredetermined oscillation means. Thus, a plurality of pulse outputsignals of different frequencies, which fit characteristics of aswitching power supply circuit and whose operation timings aresynchronized, are obtained.

Thereby, a plurality of switching power supply circuits of differentproperties, for example, switching power supply circuits of the ordinaryrectification type and the synchronous rectification type can be drivenand controlled under suitable switching conditions respectivelycorresponding thereto. Moreover, a low frequency switching beat can beprevented from occurring in the control device and in the power supplyunit.

Consequently, when applying the control device of the present inventionto a power supply unit, both of the miniaturization and the increasingof the efficiency of a power supply unit can be attained by achieving agood balance therebetween without trading off one of the miniaturizationand the increasing of the efficiency thereof.

Although the preferred embodiments of the present invention have beendescribed above, it should be understood that the present invention isnot limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the spirit of theinvention.

The scope of the present invention, therefore, should be determinedsolely by the appended claims.

What is claimed is:
 1. A pulse-width modulation power supply controldevice of a multi-channel type, comprising:an oscillator providing anoutput signal having a predetermined frequency; a plurality of controlsystems providing respective pulse output signals for respectivelycontrolling a plurality of power supply circuits independently of oneanother, said plurality of control systems receiving said oscillatoroutput signal to synchronize said pulse output signals; and a frequencydivider means coupled to at least one of said plurality of controlsystems for changing a pulse frequency, without changing on-duty time,of the pulse output signal of said at least one control system by 1/n,where n>1.
 2. A pulse-width modulation power supply control device of amulti-channel type, comprising:an oscillator providing an output signalhaving a predetermined frequency; a plurality of control systemsproviding respective pulse output signals for respectively controlling aplurality of power supply circuits independently of one another, saidplurality of control systems receiving said oscillator output signal tosynchronize said pulse output signals; and a frequency divider meanscoupled to at least one of said plurality of control systems for settingat least one first control system from among said plurality of controlsystems to produce a predetermined frequency pulse output signal and forsetting at least one second control system from among said plurality ofcontrol systems to produce a pulse output signal having a frequencylower than said predetermined frequency.
 3. The power supply controldevice of claim 2, wherein said at least one second control systemincludes means for independently driving a power supply circuit adaptedto a synchronous rectification system.